Post-synthesized zirconium-containing Beta zeolite in Meerwein–Ponndorf–Verley reduction: Pros and cons
•Zr-Beta zeolite with high Zr content prepared by a two-step post-synthesis method.•EXAFS revealed the existence of some ZrOZr bonds in Zr-Beta with Si/Zr 12.5.•Post-modified Zr-Beta formed active MPV catalysts for bulky substrates and dione.•Post-synthesized Zr-Beta is more susceptible to poisoning by water adsorption.
Zr-Beta zeolite was prepared by a two-step post-synthesis method involving dealumination of Al-Beta followed by wet impregnation with Zr(NO3)4. Compared with Zr-Beta formed under fluoride-mediated hydrothermal conditions, the post-synthesized samples had smaller particle size and stronger Lewis acidity. The materials were tested as catalysts for Meerwein–Ponndorf–Verley reduction. In the reduction of 4-tert-butylcyclohexanone, it exhibited the same excellent stereoselectivity toward cis-4-tert-butylcyclohexanol (>99%) as the HF-synthesized Zr-Beta, but had a lower TOF. Because of the higher density of zirconium sites and the nanosized crystallites, it was a more effective catalyst for the MPV reduction of 1,4-cyclohexanedione, bulky aldehydes and aromatic ketones. However, it is more susceptible to poisoning by water adsorption because of its hydrophilic nature. The easily scalable synthesis method allows a faster preparation of metal-substituted Lewis acid zeolites, although differences in textural and chemical properties should be taken into consideration when the material is applied as a catalyst.
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Journal: Applied Catalysis A: General - Volume 493, 5 March 2015, Pages 112–120